Below you will find 2 different versions of our Single Channel Target Tracker Speed Sensor. The 18ADSO has a smaller magnet than the 37ADS. When you continue down the selection path, you will find it is offered in smaller housings. The 37ADSO larger magnet version will see large targets to a farther gap. Click on the box that best fits your needs, and you will be brought to the electrical option choice page.